Differential rate hydraulic fuse



June 26, 1956 c. A. sTRAYER DIFFERENTIAL RATE HYDRAULIC FUSE Filed Dec. 18, 1953 i @www United States Patent HYSRAULC US erinners- Ar strayer, Torrance, ernia, assigner miser; thidp Aircraft', Inc.,- Hawth'ome, Calif., a corporation of eriifornia Appirfn Dersrar 18, 19513, Serin N'. 398,94s` 6 claims.v (en 60:52)'

This invention relates' to hydraulic fuses land more" particularly to a hydraulic fusev adapted to detect le'ka' es andv arrest Huid' 'oW to' certain portio'r'is of a clo's'd crcdif continuous ow hydraulic system. The' system: which' the subject fuseA is associated being further chara'ctfr''ed in' that return and supplyovvv is: equal through; out the normal' operation of the' systeni.

tfu'se o the type' disclosed herein may lie utilized to eife'ctivelI 'f arrest the How of hydraulic fluid1 to' a 1`1ii1`1tralV leal-rige servo actuator of the type shown and'gdisclds'e-'d in Ul S; Patent No". 2,640,466. Arr actuator of this' tyjje Being particularly' adapted t'o operate the control surfaces of an'A aircraft.

In= an aircraft of the' aforementionedV type, that is:` one having its control surfaces operated by hydraulic? actuators positioned adjacent these surfaces, a plurality of hydraulic lines necessarily extend t'rirough the aircrafts fuselage and wings. These lines are susceptible to damage and resultingleakage of uid therefrom due tonatdal and also'y enemy gunfire' inthe' case: of military# aircraft; lf such damage should occur to certainportions off an aircrafts hydraulic system-itl is importantthatrnerisbe provided to isolate these damaged portioiis iidat ytlsame tinieimaiu'tain unda'iaged portions iiilan' operating condition.

Hydraulic fuses-of various types have been utiliz'dfil tensively toV arrest Huid ow tliroiiglilalhyd'r-lic systei in* response to= uidflow characteristics! ocr'riti`g`-tlirei-ii atA sucli tirriev as` theyl vary materiallyfroiri lior-'rlipitl ing characteristics,

flowt through a* system; Fuses oftliis-tyiefvf'illnot; hlil ever, function toV satisfactorily detect" alleilvfroiia'cri2 tinu'ou's" owsystern under certain cofnklitions- T is Figura? thatlitf willnot causea greater flowI through tHe syst'eii than th'e'systeni isfexpe'ctedto carry-during norilloperatl i'rrg conditions; Such( aV condtiorimay' dvei'p iii; the Hydraulic lines conductingeiiidtooi fr a: ser actuator An object o'Eth'is invention? isto 'provide' a hydraulic fuse Which'fniay be" easily installed" at any-'point inra hydraulic s'ysteiri,A` thersubject fuse'functioning automti# cally to.' block uid 'tlow tofc'ertain 'portion'sf'of =tlre+`systeni `should a rupture occur therein:

sufoject fuse auforat'iclly reset ng n 2,751,751 t Patented Jurre 26, 1956 Another object ofY this invention is to provide a liy draulic fuse which automatically functions t o kgl n :l lflui iivv to certairr portions of a hydraulic systern with which it is associated at such times as differencesoccur in the fiuid-ow rate at identical sections inthe pressure and return-lines of the sys-terri. Another olijct of this invention is Ato provide adlydr'auli fuse `yvliicfi functions automaticallyI to iluid oyv to certain portions of a hydraulic systeiii with which itis associated, the fuse functioningl whensubjec'itedtom certain fluid conditions occurring Within the systern. The itself at sr-11i das as the ifessufje ofthe entire systen' is reduced to atrnosliric jrfesn'srj therhy again providing a free course for: Huid the syserri. AdtHr oj'ect of invention is tir-provide ciaiilic.I fuse vQ/h'ich functions automatically' to block iiid' rlwt "arri portions .of a: hydraulic S15/stent in yy 'di if' is irisfaia when' sbjefed to r'rinni conditie ofc'cii'ing`-tfiren. However the i:uselv'villV not block rhrbngiui system du@ f6 temporary fittizi singes occurring in the systerri.

ausser tiietype dis-closed irr- {hei-listan@ the line 19 ara pressured'approximately 3000'fp. Tnet actuator 1-1-Y (described in*r then aforementioned-U'. Si patent): is of"- the neutral leakagetype; accordingly yuii iiithpres'sure' aridI return lines' is in: a c'o'n niio'si and eqiialstateoffiow diiriiig'a'llI normal operatinigfcnditioris 6fthefsyste'm.

Refern'iig nowl td' Figure'Z' for a detailed descr'itidn o'f-the hydraulic fuse" Z13-which icoiriprisesia:body"24 'prorvided Withf uid-Y inlets, outletsg'rinternai chambers; and passgeways for-the tlow'of'iuid therethrough' Thefus'e iseprovidedwith afirsti Huid inlet-25 located-infatti upper poition of its body"(withfthe fuse psitionefasslr'owrrciii Figt're" 2j, this` inlet' cormr'mnicatesI externally with` the 19 and is, therefore,-subject to the highest uid pressure P1 occurring in the system. A rst fluid outlet 27 is provided in a lower portion of the body 24, this outlet communicates externally with the actuator 11 through a pressure line 20 and is subject to a uid pressure P2. A second uid inlet 28 is provided in a side portion of the fuse communicating externally with the actuator 11 and is subject to a uid pressure P3. A second outlet 29, located in a lower portion of the fuse 23, communicates externally with the reservoir 17 and is subject to a fluid pressure P4. The pressure P3 is normally very low with respect to pressure P1. Fluid pressure P2 is slightly less than P1 and P4 is slightly less than P3, the reason for these pressure differentials and how they are achieved will become apparent as the disclosure progresses.

`Located within the yupper portion of the body 24 is a chamber 30 consisting of two cylindrical bores of different diameters but having a common axis.V The chamber 30 is closed at one of its ends by wall portions of body 24 and at its other end by a plug 33. At approximately the mid-point of the chamber a valve seat 34 is provided, at this point the chamber is reduced in size to provide the aforementioned bores of larger and smaller diameters as indicated by numerals 35 and 37, respecand 75.

extends longitudinally of rod 65 from a point adjacentpiston 64 to a point short of its end portion. The purpose of the reduced portion 68 will be apparent presently. The bore of liner 58 is divided into two chambers 69 and 70 by the piston 64.

Located in the bore of liner 59 is a piston 72 adapted to move longitudinally therein when subjected to certain fluid pressures. The piston 72 is maintained in contacting relationship with rod 65 by means of a helical spring 73 and divides the bore in liner 59 into two chambers 74 The cylindrical surfaces of pistons 64 and 72, both end portions of rod 65, and the surfaces with which they mateV are lapped so that a minimumof Ytluid will leak past these surfaces. Suitable packing rings are proie vided in grooves formed in the outer cylindrical surfaces of liners 58 and 59 and between liner 58 and'element-62 tively, The passage 25 providesfluid communication into contacting relation with valve seats by means of between line 19 and bore 35 of the chamber`30 at a point adjacent the valve seat 34.

Positioned within the bore is a valve element 38 mounted for longitudinal movement therein.V 'I'his'valve element' consists of a body portion 39, Ya conical portion ,e Y.

40, an' extending end portion 42, and a counterbore 43 extending longitudinally within its body portion. The' body portion 39 is of such configuration that it provides a sliding support for and maintains proper alignment of the'valve element within bore 35 and at the same time .ff

allows fluid to completely surround the valve element. Positioned within the bore 37 is a piston element 45 consisting ofy a cylindrical body portion 47 and a projecting endv 48 adapted to abut the end portion 42 of the valve element. cylindrical surface of the body portion 47 are lapped so that a minimum of uid will leak past these mating surfaces." The valve element 38 and element 45 are urged into contacting relationship by a spring 49 positioned between the closed end of bore 37 and the adjacent end of element and a spring 50 positioned in counterbore 43. The springs 49 and 50 are selected and preloaded so that elements 38 and 45 are caused to assume the The cylindrical surface of bore 37 and the position shown in Figure 2 at all times except when a f failure occurs in hydraulic lines 20 or 21.

Also located in the body 24, below chamber 30, is another chamber 52 consisting of bores 53 and 54. Although the bores 53 and 54 are shown as having dilcrent diameters in the instant embodiment this need not necessarily be the case. they have a common axis which is parallel with the axis of `,chamber 30. One end of chamber 52 is closed by wall portions of body 24 and at its other end by a plug 57. Liners 58 and 59 are positioned in bores 53 and 54, re-

spectively, and are located longitudinally in abutting relatudinally therein.V This assembly consists of a piston 64 and rod 65 the latter Vpassing through central .apertures formed in shoulder 60 and element 62. The plug 57 is counterbored to provide a fluid chamber 67 and also clear ance for rod 65.

to preclude the escape of uid at these locations. The diameters of the bores'in liners 58 and 59 and the'diarneters of pistons 64 and 72 are equal.

Positioned in the uid outlets 27 and 29 are identical poppet valves 77 which are adapted to move longitudinally in the outlets. These poppet valves have ya cylindrical body portion 78 contacting the walls of outlets 27 and 29 and a conical portion 79 provided with an aperture 80 at the apex thereof. The valves 77 are urged springs 81, the aforementioned valve seats being formed by the intersection of the end surfaces of outlets 27 and 29 with the cylindrical walls of fluid passageways 82 and 83, respectively'. The valves v77 may move in a down warddirection (as viewed in Figure 2), at such times as fluid pressure acting thereon overcomes the force exerted by the springs 81, until they bottom on annularv elements 84 retained in the outlets by expansion rings 86.- The poppet valves are concentrically counterbored as in-. dicated at 85 to provide suitable seats for one end of the helical springs 81. Extending through the conical wall portion of'each poppet valve is a plurality of apertures 87 which provide unrestricted fluid communicaf tion between the interior of the outlet passages 27. and 29 and fluid passages 89 and 91, respectively. The func-` tion of the valves 77, apertures 80 and 87, and springs 81 will become apparent at such time as the operation of the fuse is explained. Y l l The aforementioned passage 82 provides uid corn-` munication between the outlet 27 and chamber 69. The passage 82 also is in iiuid communication with the bore 37 of chamber 30 through a passageway 88. Fluid com munication is also provided between outlet 27 and chamber 70 through passage 89. This latter passage is provided with a restrictor 90 which restricts the ow of uid from chamber 70 for a purpose which will be explained later. The aforementioned passage 83 provides uid communication between inlet 28, outlet 29, and cham,-

These two bores are aligned so that ber 67. Additional passages in the body 24 provide ud communication between various chambers and aforemeni tioned passages as follows: passage 92 extending between passage 83 and chamber 75, passage 93 between cham ber 70 and bore 37, 1and a passage 91 between outlet V29 andchamber 74. Passage 93 communicates with bore 37 and chamber 70 at the right hand ends thereof (Figlure 2) so that this passage will not be closed by movement of either element 45 or piston 64 until they reach the extreme right end of their strokes. 2 l

Positioned longitudinally within the chamber 75 is a plunger 94 a portion of which extends exteriorly of the body 24 so thatthe plunger may be moved manually. If the plunger is moved a sutlicient distance to the left Vpiston 72 and piston assembly 63 may be maintained in their respective positions as shownV regardless of uid pressures occurring within the fuse duringexperimental procedures, that is during bleeding operations or for over.-

A portion of rod 65 is reduced in cross- Ilv riding the fuse for any reason.

' regardless of the length of its duration, would cause the .fuse to function to arrest uid fiow tothe actuator'll. Under all conditions, as the piston 64 moves to the right, fluid in escaping from chamber 70 must flow through re- Y strictor 90 in passage 89 prior to the time that it becomes ventedto return pressure by the reduced .portion 68 of -rod 65. The size of the aperture in restrictor 90 is selected according to the estimated time necessary to fill a cavity as described above, a time delay of perhaps two seconds will elapse before the valve assembly 63 has moved far enough to the right to vent chamber 70 and bore 37 to return pressure, After a surge of fluid (lasting two seconds or any predeterminedY time) the rate of flow from passage 82 will returnvto normal, hydraulic equilibrium will be reestablished with respect to piston assembly 63 and piston 72, and spring 73 will return the assembly 63Aand piston 72 to their normal position (shown in Figure 2).

While in order to comply with the statute, the invention'rhas been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprises a preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims. v

What is claimed is:

l. A'hydraulic system of the closed circuit type and in which fiuid continuously circulates during the operation thereof: said system includinga pressurized fluid source, a uid actuator, and a fuse comprising a housing portions of which define first and second fluid passages extending therethrough; predetermined portions of said passages being of identical configuration in extent and crosssection; conduit means connected to provide fluid communication between said housing, fluid source, and actuator so that fluidin circulating through said system passes sequentially through said first passage, actuator, second passage, and fluid source; a restrictor positioned in each of the identical portions of said passages adapted to effect fluid pressure drops as iiuid ows therethrough; Valve means in said first passage responsive to said pressure drops whereby said valve means allows fluid flow through said first passagewhen said pressure 'drops effected by said restrictors are equal and arrests fluid ow through said first passage when said pressure drops effected by said restrictors are unequal.

2. A hydraulic system of the closed circuit type and in Vwhich uid continuously circulates during the operation thereof: said system including a pressurized iiuid source, a fluid actuator, and a fuse comprising a housing por- 4tions of which define first and second fluid passages extending therethrough; predetermined portions of said passages being of identical configuration in extent and crosssection; conduit means connected to provide fiuid communication between said housing, fluid source, and actuator so that fiuid in circulating through said system passes sequentially through said first passage, actuator, second passage, and uid source; a valve assembly having opposed end portions in said first passage movable between a1 first position allowing fluid ow and a second position arresting fiuid How therethrough; liuid in said first passage together with fluid diverted from said first passage and resilient means exerting a combined pressureton one end portion of said valve assembly to maintain thelatter in said rst position thereof ,during normal V,operations of said system; fiuid diverted from said second position thereof during normal operations of -said system; restrictor., means located in each of the identical portions of Ysaid passages adapted to effect equal and unequal pressure drops at such times as there is equal and unequal fluid flow, respectively, through'said passages; and piston means in said housing l'responsive to said pressure drops and functioning to release fluid exerting pressure on said other end portion of said valve subsequently after'said pressure drops become unequal.

3. A hydraulic system as set forth in claim 2: further characterized by said restrictor means comprising movable valve elements; a valve seat in each of saidpassages; resilient means'urging `said valve elements'into seating engagement with said valve seats at such times as the fluid .pressure in said passages does vnot exceed a predetermined amount; fluid under pressure in said passages adapted to move said valve elements off said Y valve seats at such times as the `tiuid pressure therein exceeds said predetermined amount; and apertures in said valve elements permitting uid ow through said passages when said valve elements are seated on saidI valve seats. Y

4. A hydraulic system as set forth in claim 2: further characterized by including restrictor means delaying the release of fiuid, exerting pressures on Vsaid other end portion of said valve, for a predetermined interval of time after said pressure drops become unequal.

5. A hydraulic fuse comprising: a housing portions of vwhich define a first chamber therein; a valve seat dividing said chamber into first and second sub-chambers; a valve in said first sub-chamber movable between seated and unseated positions with respect to said seat; a first piston in said second sub-chamber dividing the latter into first and second compartments; resilient means normally acting to'maintain said valve in said unseated position and said valve and piston in abutting relation; por tions of said housing defining a second chamber therein; a partition having an aperture therein dividing said second chamber into high and low pressure fluid chambers;

a piston assembly comprising a piston and piston rod operationally mounted in said high pressure fluidchambera second piston operationally mounted in said low pressure Huid chamber; an end portion of said piston Y Y rod extending through said aperture to alternately provide a uid by-pa'ss and a fluid tight seal between adjacent ends of said high and low pressure fluid chambers according to operational positions of said piston assembly; resilient means normally acting to maintain said piston assembly in a position in which said piston rod provides said fiuid tight seal and maintains said end portion of said piston rod and said second pistonV in abutting relation during all operational positions of said assembly and second piston; a first fiuid passage extending between an exterior surface of said housing and said first sub-chamber; a second fluid passage extending between an exterior surface of saidV housing and said firstl compartment; said first and second passages and said first chamber defining a high pressure fiuid passage when said valve is in said unseated position; a low pres;- sure liuid passage extending between non-adjacent eX- terior surfaces of ,said housing; identical uid restrictors locatedin said high and low pressure uid passages; unidirectional uid flow occurring through said high andV vpassage extending between said high pressure chamber at the end thereof adjacent said partition and said high .-pressure .passage downstream with respect to said restrictor located therein; a passage extending betweensaid .second compartment at the end thereof most removed from said valve seat and said high pressure chamber at thevend-thereof adjacent said partition; a passage extend- 9 10 ing between the low pressure chamber at the end thereof chamber at the end thereof adjacent said partition and spaced from said partition and said low pressure passaid high pressure passage downstream with respect to sage up-strearn with respect to said restrictor located said restrictor located therein. therein; and a fluid passage extending between said low pressure chamber at the end thereof adjacent said par 5 References Cited in the file 0f this Patent tition and said low pressure passage downstream with UNITED STATES PATENTS respect to said restrictor located therein.

2,493,906 Wishart Jan. 10, 1950 6. A hydraulic fuse as set forth 1n clann 5. further 2,670,750 Reynolds Mar' 2, 1954 characterized by including a Huid restrictorpositioned in said fluid passage extending between said high pressure 10 

